In the prior art, for example from DE 25 49 790, it is well known to inject a liquid into the intake section of combustion engines, such as for example gas turbosets. The evaporation of the liquid cools the intake air and increases power. The effect can be boosted further if the injected liquid mass flow is selected to be so great that the intake air is no longer able to take it up, i.e. becomes supersaturated with liquid, in such a manner that at least some of the liquid only evaporates during the compression. Therefore, if liquid drops penetrate into the substantially adiabatic turbo-compressor of a gas turboset, the evaporation in the compressor results in intensive internal cooling, and the power consumption of the compressor is reduced, which can significantly increase the net power output of the gas turboset. This method has become known, inter alia, as overfogging or wet compression. In addition, purely evaporative cooling of the intake air by means of injected drops of liquid is known as fogging.
It can be established from what has been stated above that the evaporation of injected liquid can lead to a significant temperature drop upstream of the air inlet of an engine. The temperature drop is substantially dependent on the quantity of liquid evaporated specific to the air mass. A large number of factors are crucial in this respect; firstly, the evaporation is determined by the size of liquid drops injected and their vapor pressure. Furthermore, the residence time of the drops, i.e. the distance from the air inlet to the injection location, is a crucial factor. The above mentioned influencing variables are often eliminated by fixing the drop size or drop size range within tight limits and selecting the arrangement of the injection location in such a way that moisture-saturated air is present at the air inlet of the engine, i.e. the maximum possible cooling has been achieved. The mass flow of the engine is maximized in this way. Under these conditions, the cooling which can be achieved on account of the evaporation is limited substantially by the ambient conditions of the incoming air; the cooling can continue at most up to saturation of the air and is therefore dependent mainly on the entry temperature and the relative humidity of the incoming air: whereas humid, warm air undergoes scarcely any cooling through evaporation, dry and hot air is cooled to a very considerable extent.
On account of the acceleration of the flow, further cooling of the humid air flow and if appropriate the liquid drops enclosed therein take place in the air inlet of engines, for example in the compressor inlet of a gas turboset. This can lead to the harmful formation of ice. On account of the accelerating effect, under unfavorable ambient conditions ice can form even in engines which do not have any injection of liquid. In the case of power plants which are built at locations at which such ambient conditions frequently occur, therefore, what are known as anti-icing systems form part of the prior art. In this case, by way of example, warmed air from a downstream compressor stage of a gas turboset is bled off and admixed to the intake air. Other known systems warm the intake air by heat exchange.
Therefore, EP 898 645 proposes that heat and—to ensure supersaturation of the intake air—further moisture be fed to the intake air under conditions which can lead to the formation of ice. However, this requires the presence of corresponding means for supplying heat, for example an anti-icing system. However, the provision of anti-icing systems is cost-intensive, complex, and moreover a heat exchanger system in the inflow duct of an air-breathing engine takes up installation space and causes pressure losses.
U.S. Pat. No. 6,216,443 proposes that if atomizer nozzles assisted by auxiliary media are used, either steam be used as auxiliary atomization medium, or air used for atomization be suitably preheated. Furthermore, U.S. Pat. No. 6,216,443 proposes that the temperature of water to be atomized be set to 10 to 80° C., in order to influence the location at which evaporation takes place. However, the application of this teaching requires the use of atomizers which are assisted by auxiliary media, with the associated drawbacks which this is known to entail.